1. Field of the Invention
The invention relates to molding machine nozzles, and more particularly to nozzles having a straight central flow passage leading to a "torpedo" flow guide at the exit orifice, and further having heating means for the nozzle. This type of molding machine nozzle is considered quite desirable and is less expensive than a shut-off type of bushing or nozzle.
2. Description of the Prior Art
A known prior art molding machine nozzle of this type has an elongated body with a relatively long torpedo bushing threadably mounted therein. The torpedo bushing extends downwardly from its threaded position and at its tapered forward end has diverging passages which lead the plastic to a conical cavity between the end of the bushing and the surrounding mold die. The nozzle is therefore not self-contained. The die must be machined accurately to form part of the plastic flow passage, which is rather expensive and time-consuming. A heater surrounds the body and in order to have heat flow to the outer end of the torpedo bushing one must rely on heat conduction through the threaded connection after which there is axial heat flow to the end of the bushing. Therefore, it is necessary to make this prior art torpedo bushing out of heat conductive material which is thus relatively soft metal such as bronze. In use a soft material of this nature is subject to abrasive action, especially when handling plastics containing glass particles or other abrasives. The bushing must be replaced frequently and this again is expensive. Another problem with this prior art construction is that the conventional chilling of the mold die will affect the material within the conical exit passage, since one wall of this passage is formed by the mold die itself.